A rifle can include an upper and lower receiver, and can be particularly chambered to operate with rounds of a particular caliber. Such a lower receiver can include a magazine well within which an ammunition magazine can snugly engage to maintain the magazine in a static position.
A rifle designed for a particular caliber can be modified to operate with a different caliber. For example, an AR15/M4 rifle, which is typically configured to operate with a 5.56×45 mm or 0.223 Remington round, can be modified to use a 9 mm NATO round by modifying or replacing particular ones of its components, such as for example, its barrel, bolt carrier group, recoil spring, buffer, and hammer. Additionally, conversion blocks, or conversion adapters, have been provided to modify the geometry of the AR15/M4 magazine well, so as to accommodate smaller magazines.
A conversion block is a unitary piece of construction having a rectangular parallelepiped shape with a rectangular parallelepiped cavity passing therethrough. Such a block is positioned within a magazine well to effectively reduce the magazine well size so as to accommodate a smaller magazine for a smaller round size.